All-attitude cryogenic vapor vent system

ABSTRACT

Oxygen gas is vented so as to avoid overpressure in an inadvertently horizontally positioned liquid storage-gas dispensing container having top and bottom ends and being invertible between top-up normal dispensing and bottom-up normal filling positions.

United States Patent Eigenbrod 51 Feb. 11, 1975 ALL-ATTITUDE CRYOGENICVAPOR VENT SYSTEM lnventor: Lester Kurt Eigenbrod,

Indianapolis, Ind.

Union Carbide Corporation, New York, NY.

Filed: Mar. 18, 1974 Appl. No.: 452,119

Related U.S. Application Data Assignee:

Continuation-impart of Ser. No. 311,091, Dec. 1,

1972, Pat. No. 3,797,262.

U.S. Cl 62/50, 62/55, 128/203,

141/5, 222/3 Int. Cl. F17c 7/02 Field of Search 62/50, 52, 55; 128/203,

l28/DlG. 27', 141/5; 222/3 Primary E.\'aminerMeyer Perlin Ass'islanlExaminerRonald C. Capossela Attorney, Agent, or Firm-.lohn C. LeFever[57] ABSTRACT Oxygen gas is vented so as to avoid overpressure in aninadvertently horizontally positioned liquid storagegas dispensingcontainer having top and bottom ends and being invertible between top-upnormal dispensing and bottom-up normal filling positions.

10 Claims, 7 Drawing Figures JVVS/ VVVVVVW PAIENIED Y 3.864.928

SHE'ETZUFE.

F 1 sfz PATENIEI] FEB I I I975 I SHEET 3 DFB TIME IN MINUTES 9ISd38088388 IPAIENTEI] FEB! 1 I975 SHEET 5 OF 6 ALL-ATTITUDE CRYOGENICVAPOR VENT SYSTEM This application is a continuation-in-part of Ser. No.311,091, filed Dec. 1, 1972 now U.S. Pat. No. 3,797,262 in the name ofLester K. Eigenbrod.

BACKGROUND OF THE INVENTION This invention relates to a method of andapparatus for venting gas, e.g., breathing oxygen, from a cryogenicliquid storage gas supply system.

In the prior art systems for supplying breathing oxygen from a liquidoxygen source as for example described in U.S. Pat. No. 3,199,303,certain disadvantages have become apparent as the system is used in thehome or hospital for medical therapy of pulmonary and cardiac disorders.

For example, it has been impossible to completely fill the invertedliquid oxygen storage-dispensing container from the larger liquid oxygencontainer positioned beneath and connected to the first-mentionedsmaller vessel. This is because the same conduit in the smallercontainer is relied on for gas venting in both the inverted liquidfilling step and the top-up liquid dispensing step. Stated otherwise,the gas vent conduit terminates at about the midpoint of the smallercontainer so that it may be used for venting oxygen vapor when thecontainer is in the bottom-up position for filling. Accordingly, thecontainer may only be half-filled or the gas vent conduit would besubmerged. This of course means that the liquid storage volume is onlyhalf-used, an important disadvantage when one recognizes that thecryogenic liquid storage-dispensing container must be sufficiently smallfor manual handling by one person, in particular repositioning betweentop-up and bottom-up.

The aforementioned disadvantages have been overcome by the cryogenicfluid supply system described and claimed in my aforementionedapplication Ser. No. 311,091 now U.S. Pat. No. 3,797,262. An importantcharacteristic of this improved system is the dual function of certainelements. For example, the conduit means used for gas venting of thestorage-dispensing container highest zone (top-up end) to avoidoverpressure during the gas supply step becomes the liquid fill conduitmeans when the container is inverted to the bottom-up position.Cryogenic liquid is upwardly charged from the supply container throughthis same conduit into the lowest zone (top-down end) of the invertedstorage-dispensing container. Also, the conduit used for liquidwithdrawal from the lowest zone (bottom-down end) of thestorage-dispensing container during the gas supply step becomes the gasvent conduit during the liquid charging step when the container isinverted. The atmospheric vaporizer used for vaporizing liquiddischarged from the storage-dispensing container during the gas supplystep is used to warm the cold vent gas during the liquid charging step,thereby avoiding the discharge of cold gas in the close vicinity of theuser. This interchangability of function facilitates an extremely lightand compact system well-suited for supplying breathing oxygen to peoplewho must move about while carrying the storage-dispensing container. ltalso permits complete filling of the storage dispensing container withcryogenic liquid.

Notwithstanding the advantages of this cryogenic fluid supply system(hereinafter referred to as the invertible dual vent system), it has aspecific unique disadvantage. If the container is inadvertently placedin a non-vertical position (i.e., either inclined or horizontal) whennearly or completely filled with cryogenic liquid, then the internalends of both the gas vent-liquid fill conduit (terminating in thecontainer normally top end) and the liquid withdrawal-gas vent conduit(terminating' in the container normally bottom end) may be immersed inliquid. Such immersion reduces drastically the pressure relievingcapabiligy of the venting circuits and may produce hazardousoverpressures. Moreover, discharging of cold cryogenic liquid couldresult with potential risk to the user and with attendant high loss ofstored fluid.

In the prior art systems for supplying breathing oxygen from liquidoxygen, these dangers were not present because the gas vent conduit isalways in the interior vapor space regardless of the overall position ofthe liquid storage dispensing container. Liquid was thereby preventedfrom being discharged through the gas vent conduit; The importance ofthese features will be appreciated by a brief consideration of thepractical usage of such oxygen supply systems. The invertible liquidoxygen storage-dispensing container is designed to be carried by amoving patient and consequently is relatively small, as for examplecontaining only about 1.6 pounds of liquid oxygen. Considering the smallsize of this container, any liquid venting would be highly undesirableand represent an important loss of breathing oxygen capacity. Even moreimportantly, such venting is hazardous to the user because of thepossibility of severe burns from skin contact with the liquid oxygen.Also, venting ofliquid could result in highly localized oxygenconcentrations as the liquid vaporizes with the danger of ignition ofnearby combustible materials.

It might appear that the cold fluid venting problem of such horizontallypositioned invertible dual vent systems could be solved by simplyinstalling automatic closure means on both gas vent conduits andactivating such closure means when the container is displaced from thevertical. This however is not a practical solution to the problembecause of the dual functions of these conduits, i.e., both conduits areemployed when the container is inverted in the bottom-up fillingposition. In addition with both conduits closed there would be noprovision for relieving over-pressure due to evaporation of thecontained liquid.

Another possible approach to the venting problem would appear to bemerely increasing the venting capacity of the safety relief meansprovided on the gas vent-liquid fill conduit, and by passing the fluidthus vented through vaporizing and superheating apparatus external ofthe container. The capacity of the safety relief means and itsassociated vaporizer could be made sufficiently large to appropriatelylimit over-pressure even when the internal end of the gas vent-liquidfill conduit is inadvertently submerged. However, the physical size andweight of such a vaporizersuperheater would become prohibitively large.The magnitude of the increase in capacity of the safety relief meanswhich is needed in order to properly function with the inlet endsubmerged can be better appreciated from the following comparison.Assume that one unit volume of cryogenic fluid is removed from acontainer at 50 psig and is warmed at this pressure to C for venting. Ifthe unit volume is removed as liquid, then its volume at 50 psig afterwarming will be over 50 times greater than if the unit volume has beenremoved as vapor. Moreover, the unit volume of liquid requires about 100times more heat for warming to 70F than does one unit volume of vapor.This approach to the venting problem would add excessive weight and bulkto a small portable oxygen breathing apparatus. It is estimated that thesize of a practical breathing apparatus would be necessarily increasedabout 30-35 percent by such approach.

An object of this invention is to provide an improved invertible dualvent cryogenic fluid supply system which will vent only gas ifinadvertently placed in a non-vertical position.

Another object is to provide such a cryogenic fluid supply system with agas venting system which does not necessitate a larger apparatus.

Other objects and additions will be apparent from the ensuing disclosureand claims.

SUMMARY This invention relates to an all-attitude pressure relief systemfor invertible dual vent cryogenic fluid supply systems as for exampleused for portably dispensing oxygen breathing gas.

1n this cryogenic liquid storage gas supply system a thermally insulatedcryogenic liquid storage-dispensing container is included; it has topand bottom ends and is invertible between top-up dispensing andbottom-up filling positions.

Gas vent liquid fill conduit means are also provided with a first endterminating in the container top end and a second end outside thecontainer top end. This system further includes liquid withdrawal-gasvent conduit means with a first end terminating in the container bottomend and the second end outside the container top end. An invertibleliquid vaporizing-gas vent control circuit is located outside thecontainer and joined at a first inlet end to the liquid withdrawal-gasvent conduit means second end. This circuit includes a first atmosphericvaporizer, and gas flow regulating means between the first atmosphericvaporizer and the gas discharge other end of the circuit.

The apparatus of this invention includes an allattitude pressure reliefsystem for the container comprising (a) first higher pressure reliefmeans between said first atmospheric vaporizer and said gas flowregulating means, (b) branch conduit means having one end in flowcommunication with the gas-vent-liquid fill conduit second end, (c)second flow restriction-pressure relief means in the branch conduit (b)constructed to vent gas at lower abs. pressure than said first pressurerelief means and at a maximum rate between 3 and 25 times the normalevaporation rate from the container, and (d) a second atmosphericvaporizer in flow communication at its inlet end with the branch conduitone end and in flow communication at its discharge end with the secondflow restriction-pressure relief means. The second atmospheric vaporizeris constructed with a heat transfer capacity not greater than one-thirdthe first atmospheric vaporizer heat transfer capacity and alsosufficient to vaporizer cryogenic liquid entering its inlet end and todischarge warmed gas at its discharge end at a rate between 1.04 and1.30 times said maximum rate.

In another aspect of this invention a method is provided for supplyinggas from a thermally insulated cryogenic liquid-storage-dispensingcontainer having top and bottom ends and being invertible between top-updispensing and bottom-up filling positions and wherein during the gassupplying step, cryogenic liquid is flowed by overhead vapor pressureupwardly from the lowest zone of the container, discharged from thecontainer top end and vaporizer by atmospheric heat to form gas supply.More particularly, in the improved method and in the top-up dispensingposition: (a) when gas is not being supplied vapor is vented through apassage from the highest zone of the container at flow-restrictedmaximum rate between 3 and 25 times the normal evaporation rate from thecontainer, warmed by atmospheric heat and discharged when the containerpressure is above a first lowest superatmospheric relief pressure. Also(b) when gas is being supplied, cryogenic liquid is flowed by overheadvapor pressure upwardly from the lowest zone of the container anddischarged from the latters top end. The so-discharged liquid isvaporized by atmospheric heat, warmed and withdrawn as the gas supply,and vapor is simultaneously vented in accordance with step (a).

When the container is in a non-vertical position such that liquid flowthrough the passage of step (a) and if the container gas pressure risesabove the first lowest superatmospheric relief pressure, first liquid isdischarged from the normally top end at a first lower flowrestrictedrate, vaporized and warmed to ambient tem perature and then released atpressure above the first lowest superatmospheric relief pressure. Thecontainer pressure rises to a second higher superatmospheric reliefpressure which is between 1.08 and 1.75 times the first superatmosphericrelief pressure on an absolute basis, second liquid is simultaneouslydischarged from the normally bottom end of the container at a secondhigher rate, vaporized and warmed to ambient temperature and finallyreleased at pressure above the second superatmospheric relief pressure.

As used herein, atmospheric vaporizer means a heat exchanger with aclosed passage for receiving cryogenic liquid and discharging gas andfor supplying latent heat of vaporization to the cryogenic liquid onlyfrom the ambient atmosphere rather than from a second fluid flowing in asecond closed passage. Also, heat transfer capacity of the first andsecond atmospheric Vaporizers refers to their external surface areassince the latter comprises the controlling resistance of heat transfer.When one or both of the atmospheric vaporizers is provided with externalsecondary heat transfer surface such as fins, then heat transfercapacity refers to the equivalent primary surface area of the vaporizer.That is, such secondary surface area is converted to equivalent primarysurface area by applying fin efficiency factors in the well-knownmanner.

As used herein, normal evaporation rate means the average rate at whichstored oxygen liquid is vaporized internally of an insulated containerand the gas discharged therefrom solely to compensate for heat inleakagefrom the surroundings. The determination of the normal evaporation rateis made by employing a container having thermal insulation of normaleffectiveness, filling the container to normal full level, p0- sitioningthe container in normal top-up orientation, allowing the container andcontents to thermally equilibrate at an internal pressure substantiallyequal to the minimum intended operating pressure for liquid oxygendischarge, and measuring the rate at which gas is vented. The conditionof thermal equilibration is assumed to be reached when the initiallyhigh vent rate after filling has subsided to a steady, uniform rate.After equilibration, the vent rate may be measured directly byinstantaneous rate of gas flow and several such measurements arepreferably taken at spaced intervals of time and averaged.Alternatively, the container with contents may be carefully weighed atthe beginning and end of a time period of uniform venting and the weightchange may be ratioed to the lapsed time to obtain an average vent rate.The average vent rate so determined is then converted to normaltemperature and pressure, i.e., 1 atmosphere pressure and 70F, to obtainthe normal evaporation rate of the container.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic drawing taken incross-sectional elevation of a cryogenic liquid storage-dispensingcontainer and liquid vaporizing-gas discharge control circuit in thetop-up position with the all-attitude gas relief circuit of thisinvention.

FIG. 2 is a schematic drawing taken in cross-sectional elevation of theFIG. 1 container, liquid vaporizing-gas discharge gas relief circuit inthe inverted bottom-up position and joined to a cryogenic liquid supplycontainer, during the liquid charging the gas vent step.

FIG. 3 is a schematic drawing in cross-sectional elevation of apreferred liquid vaporizing-gas vent control circuit in the top-upposition, and differing from the FIG. 1 embodiment by the employment ofpneumatic control and a four-way atmospheric gas vent valve means.

FIG. 4 is a graph showing the oxygen gas pressure DESCRIPTION OF THEPREFERRED EMBODIMENTS Referring now more specifically to the drawings,FIG. 1 illustrates a vertical cryogenic liquid storagedispensingcontainer 10 and all-attitude gas relief circuit during the gassupplying period. Container 10 comprises an outer casing 11 and an innervessel 12 for holding the cryogenic liquid, with an evacuable spacetherebetween preferably filled with thermal insulation 13 as for examplethe alternate layers of aluminum foil and glass fiber sheets describedin US. Pat. No. 3,007,596 to L. C. Matsch. Container 10 has top andbottom ends 14 and 15, respectively, and is invertible between top-upand bottom-up positions. It is preferably sufficiently small for manualmovement and inverting. Gas vent-liquid fill conduit means 16 has afirst end 17 extending through and terminating in the normally top-upend 14 of container 10 and a second end 18 outside and above suchnormally top-up end. Second coupling means 19 is joined to and abovesecond end 18 when container 10 is in the top-up position.

Liquid withdrawal-gas vent conduit means 21 also extends through thecontainer top end 14 with the first end 22 thereof terminating in thenormally bottomdown end 15 above the inner vessel base. The second end23 of liquid withdrawal-gas vent means 21 is outside and above thenormally top-up end 14 of container 10. Invertible liquid vaporizing-gasvent control circuit 24 comprises liquid sensing means 25 joined to theliquid withdrawal-gas vent means second end 23, first atmosphericvaporizer 26 joined at one end to the liquid sensing means 25, andatmospheric gas vent valve means 27 joining the other end of theatmospheric vaporizer.

Signal transmitting means are also provided for automatically closingatmospheric gas vent valve means 27 in response to the sensing of liquidby the liquid sensing means. Such means may for example be based on athermistor 25a and comprise electric signal receiving wire 28,controller 29, and electric signal transmitting wire 30 joined to asolenoid-operated vent gas valve 27. More particularly, controller 29contains a relay and low amperage current flows from the relay coilthrough wire 28 and thermistor 25a. With only gas flow around thermistor25a its resistance is 100-300 ohms but when wet with cryogenic liquidits resistance increases to 6,000-l0,000 ohms. This increased resistancetrips the controller 29 relay so that its contacts open in the wire 30circuit to vent valve 27, closing same.

During the gas supplying period, the user may select gas (e.g., oxygen)supplying rates by manually controlling the gas flow regulating means asfor example supply valve 31 located between the first atmosphericvaporizer other end (opposite liquid sensing means 25) and gas ventvalve 27. When valve 31 is open, overhead vapor pressure forcescryogenic liquid upwardly from the container lowest zone or end 15 andthrough liquid withdrawal-gas vent conduit 21, past liquid sensing means25, and through first atmospheric vaporizer 26 where the liquid isvaporized.

The all-attitude gas relief circuit includes first pressure relief valve32 in branch conduit 33 downstream of first atmospheric vaporizer 26.Stated otherwise, first pressure relief valve 32 is in communicationwith the conduit system between the other end of atmospheric vaporizer26, atmospheric vent valve 27 and gas supply valve 31, and isconstructed to release gas at superatmospheric pressure.

The gas relief circuit also includes branch conduit 34 in flowcommunication at its inlet end with gas ventliquid fill conduit 16, andhaving second flow restriction pressure relief means 36 thereinconstructed to release gas at lower superatmospheric pressure than firstpressure relief valve 32 and at maximum predetermined rate between 3 and25 times the normal evaporation rate from the container. Secondatmospheric vaporizer 35 is in branch conduit 34 with its inlet end inflow communication with the branch conduit inlet end and with itsdischarge end in flow communication with the second flow restrictionpressure relief means 36. Second atmospheric vaporizer 35 is constructedwith a heat transfer capacity sufficient to vaporize liquid entering itsinlet end and to deliver warmed gas at its discharge end at a ratebetween 1.04 and 1.30 times the maximum flow rate through second flowrestriction pressure relief means 36.

Although flow restriction-pressure relief valve 36 illustrated in FIG. 1may comprise the major flow restriction pressure relief means, otherstructural components may be used in addition thereto as performing partof the same function. For example, a separate flow restriction element36a such as an orifice or porous member may be placed at the dischargeend of the conduit 34, downstream valve 36. If the passage size ofconduit 34 and vaporizer 35 are relatively large, e.g., the same sizediameter as branch conduit 33, a separate flow restrictor element isneeded in order to limit flow to within 3 and 25 times the normalevaporation rate and to keep the required length of vaporizer 35 small,consonant with a small overall apparatus size. Flow restrictor 3611 mayalternatively be located upstream rather than downstream pressure reliefmeans 36 and will provide the same overall system performance, but thedownstream location is preferred since it prevents introduction ofatmospheric contaminants such as dust through the conduit 34 dischargeend.

In preferred practice of the invention, a fixed flow restriction element36a is provided in series with relief valve 36 in order to provide morepositive assurance that the heat transfer capacity of the secondatmospheric vaporizer will not be exceeded. For many relief valves, thesize of the flow passage through the valve increases with pressure aboveits set point such that its effectiveness as a flow-limiter isdiminished. With a fixed restriction in the circuit, an increase invalve opening transfers a larger fraction of the total circuit flowresistance to the fixed restriction, thereby preventing an overloadedcondition in the relief circuit.

in the practice of this invention second atmospheric vaporizer 35 willbe limited by space and weight considerations to a heat transfercapacity not greater than one-third and preferably not greater thanone-fifth the capacity of first vaporizer. With such limitation theoverall size of the portable package is not greatly increased thereby,yet only gas venting can be assured if the package is inadvertentlypositioned horizontally. To insure that the second vaporizer capacity isnot exceeded, the second flow restriction-relief means 36 is constructedto limit the maximum rate of flow to a value below that which wouldexceed the vaporizer capacity. Since the ambient air side of thesevaporizers controls the fluid (heat transfer) capacity, the outersurface areas may be used for this comparison.

It will also be understood that for safety reasons a high pressurebursting disk 38 may be located in conduit 34 between second vaporizer35 and second flow restriction-pressure relief means 36. Alternativelythe bursting disk may be positioned in gas delivery conduit 33immediately upstream gas delivery valve 31, but the former is thepreferred location. The reasons for this preference are: l the burstingdisk is directly in communication with the gas phase in the containertop-up position, (2) the length of delivery gas conduit 33 is minimizedand (3) the bursting disk is maintained at ambient temperature duringoperation so that its accuracy is not impaired.

it has previously been indicated that according to the apparatus of thisinvention, the second flow restrictionpressure relief means 36 isconstructed to vent gas at lower pressure than first pressure reliefmeans 32 and at maximum rate between 3 and 25 times the normalevaporation rate (NER) from the container, preferably between 5 andtimes the NER. Similarly, in the instant method in the top-up dispensingposition vapor is vented through a passage from the highest zone of the8 container at flow restricted maximum rate between 3 and 25 times theNER and preferably between 5 and 20 times the NER.

The lower pressure portion of the all-attitude gas relief circuit isprimarily intended to avoid overpressure when container 10 is in itsnormal top-up fluid dispensing position and with a reasonably highquality thermal insulation 13 and low absolute pressure in the evacuablespace on the order of 1 micron Hg. Under these circumstances the maximumvent gas rate need only be about three times the NER so as to insureprotection against the possibility that the insulation vacuum might bepartially lost due to leakage, such that the evaporation rate increasessubstantially above the NER. It will of course be noted that the higherpressure first relief means 32 serves as backup for lower pressuresecond flow restriction-pressure relief means 36, but operation of thelatter should be avoided except in instances when unexpected cryogenicfluid vent loads occur, i.e., when container 10 is inadvertently placedin a nonvertical position. This is because such operation rather quicklyreleases virtually the entire contents of the container, tends to causefrosting (and loss of effectiveness) of first va'porizers 26 externalsurface and may even cause freeze up of relief means 32.

The maximum vent gas rate of second flow restriction-pressure reliefmeans 36 does not exceed 25 times the container NER so as to avoid thenecessity of a prohibitively large and heavy second atmosphericvaporizer 35 which would not be portable. The maximum vent gas raterange of between 5 and 20 represents a preferred balance of theforegoing considerations.

Another requirement of the instant apparatus is that the secondatmospheric vaporizer be constructed with a heat transfer capacity notgreater than one-third and preferably not greater than one-fifth thefirst atmospheric vaporizer heat transfer capacity. The latters capacityis determined by the need for warming cold vapor discharge fromcontainer 10 in the top-down liquid filling position, thereby avoidingpressure buildup and release of cold vapor during the fast liquid fill,i.e., less than about 4 minutes. The first atmospheric vaporizer 26 mustbe relatively large, e.g. 17 feet of unfinned A inch tubing, andoccupies most of the available space within the case surroundingcontainer 10. Under these circumstances second atmospheric vaporizer 35can only be a small fraction of the first vaporizer size or the overallassembly becomes so large and heavy as to be non-portable.

in the method of this invention and with the container in a non-verticalposition, it has been stated that when the container pressure rises to asecond higher superatmospheric relief pressure between 1.08 and 1.75times the first atmospheric relief pressure on an absolute basis andpreferably between H5 and 1.4 times the first relief pressure, secondliquid is discharged from the normally bottom end simultaneously withthe first liquid discharge from the normally top end of the container.The aforementioned lower limit of 1.08 and preferably 1.15 is needed toinsure that the higher pressure first relief valve 32 will operate onlywhen the pressure relieving capability of the lower pressure secondrelief means 36 has been exceeded. This lower limit reflectsmanufacturing and adjustment tolerances of commercially availablepressure relief devices.

The aforementioned upper limit of 1.75 and preferably 1.4 is due to theincreased mass flow through branch conduit 34 and the low pressurerelief circuit when the container pressure rises to the second highersuperatmospheric relief pressure. if the pressure difference between thesettings of the two relief valves 32 and 36 is too great and first end17 of gas vent-liquid fill conduit 16 is submerged in cryogenic liquid,the heat transfer capacity of second atmospheric vaporizer 35 would beexceeded. This would be due to the increased flow, resulting in cold gasreaching and possibly freezing second relief valve 36.

it will also be recalled that in the present apparatus, the secondatmospheric vaporizer is constructed with a heat transfer capacitysufficient to vaporize cryogenic liquid entering its inlet end anddischarge gas at rate between 1.04 and l.30 times the maximum vent rateof the second flow restriction-pressure relief means 36, and preferablybetween 1.08 and 1.2 times the maximum vent rate. The increase inpressure between the set points of the two relief devices also producesan increase in flow rate through the low pressure relief circuit, asdiscussed in the previous paragraph. This flow rate increase is mostlikely to occur when the container is in a non-vertical position andfirst end 17 is immersed in liquid. The flow rate ratio lower limitreflects the need for an adequate difference between the reliefpressures of the two devices as previously discussed. The flow rateratio upper limit is to avoid exceeding the heat transfer capacity ofsecond atmospheric vaporizer 35 due to increased liquid flow.

FIG. 2 illustrates the step of charging storagedispensing container withcryogenic liquid from supply container 40. The latter is similar inbasic construction to container 10 but usually larger, and comprisesouter casing 41 and inner vessel 42 for holding the cryogenic liquid,with an evacuable space therebetween preferably filled with thermalinsulation 43. Cryogenic liquid may be introduced to supply container 40through feed valve 44 and inlet conduit 45, also provided with safetyrelief valve 46. This liquid is prefera bly prewarmed prior to or duringintroduction such that it is saturated at the operating pressure desiredfor discharging same into container 10 as for example described in US.Pat. No. 2,951,348 to Loveday et a]. For example, if the desired oxygenvapor pressure is 40 psig, saturated liquid oxygen at -l68C (105K) maybe introduced to a supply container of 17.5 liters liquid capacity andprovided with 0.4 inch of aluminum foilglass paper alternate layerinsulation of 0.040 X 10' Btu/hr. X ft. X F/ft. thermal conductivity inthe evacuated space at a density of about 60 foils/inch. Alternatively,subcooled liquid oxygen may be introduced to the same supply containerand upon mild, occasional agitation of the supply container, sufficientsaturated pressure can be eventually obtained to operate the system. Ifsuch pressure is substantially lower than 40 psig than an appropriaterevision must be made in the set point of the liquid sensor when thepneumatic system of FIG. 3 is employed (discussed hereinafter indetail).

As an alternative for insuring that the vapor pressure in container 41is sufficient to discharge the cryogenic fluid into container 10 at thedesired temperature and pressure, means may be provided for controllablyintroducing external heat to container 41. More particularly when and ifthe vapor pressure drops below a predetermined level, liquid may becontrollably withdrawn through conduit 50 by opening valve 51 therein,vaporized in atmospheric vaporizer 52 and returned as vapor to the topend of inner vessel 42. Mild agitation of the contents will avoidStratification and obtain a uniformly saturated condition throughout theliquid body. It should be understood that the aforedescribed pressurebuilding circuit 50-52 is not required if the cryogenic liquid isintroduced to container 40 in the prewarmed saturated container.

For charging of container 10, the latter is inverted and positioned withits top end in flow communication with supply container 40. The latteris provided with liquid discharge conduit 53 having first end 54terminating in the bottom end of inner vessel 2 and second end 55outside the container top end. First coupling means 56 is provided atthe conduit second end 55 and joined to second coupling means 19preferably in a manner such that fluid communication is established onjoining.

Cryogenic liquid flows upwardly through conduit 53, second couplingmeans 56, first coupling means 19, and vapor vent-liquid fill conduitmeans 16, and merges from the latters first end 17 into the lowest zoneof inverted container 10 which is its normally top end 14. The conduit16 previously used for vapor venting dur ing the liquidstorage-dispensing and gas supply step is now used for liquid filling.

As liquid transfer progresses, cryogenic vapor in the highest zone ofinverted container 10 which is its normally bottom end 15, must bevented in order that the pressure in 15 will be lower than that incontainer 41 by an amount greater than the hydrostatic head to beovercome. To insure that such pressure differential exists, vapor fromcontainer 10 is admitted to the first end 22 of liquid withdrawal-gasvent conduit 21 for flow through inverted circuit 24 past liquid sensingmeans 25, further warming in first atmospheric vaporizer 26 and releasedthrough opened atmospheric gas vent valve means 27. Accordingly, duringthe liquid charging step the invertible circuit 24 previously used forliquid discharge and vaporization during the gas supply step is now usedfor gas venting.

The cryogenic fluid discharged from inverted container 10 during theliquid charging step is sensed by element 25a. When container 10 is fullof liquid, the latter will start to flow into the inverted liquidvaporizing-gas vent control circuit 24. Element 25a detects the presenceof liquid prior to its reaching first atmospheric vaporizer 26, and thedetection is used as a signal to automatically close gas vent valvemeans 27, i.e., through electric signal receiving wire 28, controller29, and electric signal transmitting wire 30. Once vent valve means 27is closed the pressure differential between containers l0 and 40 willdrop to a value substantially equal to the hydrostatic head produced bythe difference between the liquid-gas interfaces in the two containers.When this occurs liquid transfer ceases. First and second coupling means56 and 19 respectively are now disconnected, container 10 is returned toits normally top-up position and the previously described gas supplystep is reinstated. First and second coupling means 56 and 19 arepreferably of the type that automatically close when disconnected sothat shut-off valves are not needed in gas vent-liquid fill conduitmeans 16 and liquid discharge conduit 53.

FIG. 3 illustrates another and preferred liquid charging terminationcontrol system based on the generation of a pressure rise on liquidsensing in circuit 24, and pneumatic rather than electric signaltransmission to gas vent valve 27. The cryogenic liquidstoragedispensing container 10, gas vent-liquid fill conduit means 16,and liquid withdrawal-gas vent conduit means 21 are substantiallyidentical to FIG. 1 and operate in the previously described manner.

The FIG. 3 liquid vaporizing-gas vent control circuit 24 includessmaller size control fluid conduit 60 joined at one end as liquidsensing means 25 to the second end 23 of liquid withdrawal-gas ventconduit 21 outside and above the normally top end 14 of containerupstream of first atmospheric vaporizer 26. A smaller third atmosphericvaporizer 62 is provided in control fluid conduit 60 and a first flowrestrictor as for example orifice 63 is positioned between the one end25 of conduit 60 and secondary atmospheric vaporizer 62. Second flowrestrictor 64 is located between third atmospheric vaporizer 62 and theother end 65 of fluid control conduit 60. Such other end 65 is joined toatmospheric gas vent valve 27, preferably the illustrated four-way type.With such a valve, during the cryogenic liquid charging of container 10gas may be simultaneously vented through a major vent gas circuit and aminor vent gas circuit. When the liquid charging is completed, thefour-way valve 27 closes the two separate vent gas circuits fromcommunication with the atmosphere by interconnected same. Moreparticularly, a first flow passage is established through the valveconnecting first inlet port 27a and first outlet port 27b, and permitsventing of a major portion of the vent gas through primary atmosphericvaporizer 26. A second flow passage is also established connectingsecond inlet port 27c and second outlet port 27d, and permits venting ofa minor vent gas portion through control fluid conduit 60. To terminatethe liquid charging, the flow passages are realigned so that first andsecond inlet ports 27a and 27c are connected. A small diameter pressuretransmitting conduit- 66 has one end joining control fluid conduit 60between flow restrictors 63 and 64 and preferably between thirdatmospheric vaporizer 62 and second flow restrictor 64, and the otherend joined to pneumatic actuator 67 mechanically coupled to four-wayatmospheric gas vent valve 27. First flow restrictor 63 and second flowrestrictor 64 are sized so that a pneumatic signal is transmittedthrough conduit 66 to close valve 27 when the pressure in control fluidconduit 60 intermediate third atmospheric vaporizer 62 and second flowrestrictor 64 rises to a predetermined level.

When the FIG. 3 container 10 and liquid vaporizing gas vent controlcircuit 24 are in the inverted bottomup position and connected tocryogenic liquid supply container 40 in a manner analogous to FIG. 2,four-way valve 27 is manually set to the open position. The vent fluidsflow from inverted container 10 through both the major and minor ventgas circuits to the atmosphere. During this cryogenic liquid chargingstep, the resistance to fluid flow in the minor vent gas circuit is muchgreater than that in the major circuit due to first and second flowrestrictors 63 and 64. Accordingly, most of the venting gas flowsthrough first vaporizer 26. During the succeeding gas supplying step,all of the cryogenic liquid discharged from top-up container 10 flows tofirst vaporizer 26.

When the inverted FIG. 3 container 10 is filled with cryogenic liquid,the latter begins to exit through both the major and minor ventcircuits. Again, most of the liquid flows to the major circuit includingfirst vaporizer 26, is vaporized and released to the atmosphere as awarm gas. Some of the overflowing liquid is carried into the controlfluid conduit 60. Compared to the previously flowing cold gas, firstflow restrictor 63 passes relatively more mass of fluid as liquid with amuch reduced pressure drop, and supplies this liquid to the thirdatmospheric vaporizer 62. The liquid is vaporized and warmed rapidlytherein and increases several hundred fold in volume. Suddenly, a muchlarger volume of gas flows to the second flow restrictor 64 which nowbecomes the major resistance in conduit 60. The pressure in this conduitbetween first and second flow restrictors 63 and 64 will rise abruptlyto balance the new flow of inlet liquid (instead of inlet gas). Thispressure rise is transmitted by conduit 66 to pneumatic actuator 67which operates to set four-way gas vent valve 27 to the closed position.When this occurs, the pressure levels throughout the supply andstorage-dispensing containers l0 and 40 and the interconnected fluidconduits will equalize (except for the aforementioned hydrostatic head)and liquid charging is stopped.

The elements of the liquid vaporizing-gas vent control circuit 24 aresized and selected so that the necessary pressure level to actuate thepneumatic system for closing gas vent valve 27 is readily and dependablyobtained well within the limitations of acceptable pressures forcontainers 10 and 40. Further, the circuit elements are preferably sizedso that the liquid sensing response is sufficiently fast to preventcryogenic liquid spillage from vent valve 27. For example, the firstflow restrictor 63 is preferably sized so that when cryogenic liquidreaches the liquid vaporizing gas vent control circuit 24 at the end ofliquid charging, only a small quantity of liquid passes through therestrictor and it does not exceed the capacity of third vaporizer 62.The second flow restrictor 64 downstream vaporizer 62 is sized toprovide sufficient flow resistance to the nowvaporized liquid so thatthe gas pressure level sharply rises to the desired level between thetwo flow restrictors thereby generating a reliable signal.

The advantages of the invention were demonstrated in a test wherein aliquid oxygen storage-dispensing container and the all-attitude gasrelief circuit as schematically illustrated in FIG. 3 and shown in theassembly drawings of FIGS. 5-7 was placed in the horizontal position.The container was provided with alternate layers of glass fiber paperand aluminum foil insulation wrapped around the inner vessel as thermalinsulation to be provide about 14 layers in a thickness of aboutthree-eights inch. The insulation space was also provided with molecularsieve zeolite adsorbent and hydrogen-selective getter and evacuated toan absolute pressure ofless than 1 micron Hg. The thermal conductivityof the insulation at this pressure was about 2.5 X 10 Btu/hr. X ft. X F.The oxygen gas pressure within the container and the container weightwere both monitored with respect to time, and the results areillustrated in the FIG. 4 graph. In brief, the container held about 3.35lbs oxygen when full, and its total weight was about 15.7 lbs. Secondatmospheric vaporizer 35 (substantially the entire length of lowpressure relief conduit 34) comprised about 24 inches of 0.25-inch outerdiameter, 0.032-inch thick aluminum tubing including second vaporizer'35. Low pressure second relief valve 36 was set at 62 psig, and flowrestrictor ele- FLOW CHARACTERISTICS PRESSURE (PSlG) FLOW RATE UpstreamDownstream Liters Per Minute Gas (NTP) The first atmospheric vaporizer26 was formed of 0.25-inch outer diameter, 0.032 inch thick aluminumtubing, so that the second atmospheric vaporizer heat transfer capacitywas about 0.12 times the first atmospheric vaporizer capacity (based ona of outside surface areas). The high pressure relief valve 32 was setat 67 psig. However, it is preferred to maintain a Wider spread inpressure settings between the first and second relief valves 32 and 36,and typical settings are 68 psig and 52 psig. respectively.

Referring now more specifically to the FIG. 4 graph about 1 hour wasrequired after filling for the horizontally aligned container pressureto reach the 62 psig. setting of low pressure second relief valve 36 asrepresented by vertical dotted-line line (a). During this initial periodthere was of course no loss of stored oxygen so that the total weight(lower) curve was horizontal. During the succeeding 1 /2 hour periodaverage oxygen boil-off loss rate through this valve was 1.52 litersoxygen (NTP) per minute and the container pressure increased to 67 psig.the setting of high pressure first relief valve 32. The latter opened,as represented by vertical dotted line (b), and both relief valves wereopen for the ensuing one hour-and the average oxygen boil off loss ratethrough the valves was 6.84 liters oxygen (NTP) per minute. After atotal elapsed time of 210 minutes as represented by vertical dotted line(0), the second end 22 of liquid withdrawal-gas vent conduit 21 was nolonger immersed in liquid oxygen. After a total elapsed time of 254minutes as represented by vertical dotted line (d) the oxygen boil-offrate was equal to the normal evaporation rate at 62 psig for thecontainer in the vertical top-up position.

No liquid oxygen was vented at any time during the aforedescribed test.The total boil-off of gas amounted to 1.8 lbs. 0 a low of about 54percent was thus sustained but 1.55 lbs. 0 remained in the container.This remaining amount of liquid is equivalent to over 1 hours breathingatmosphere at the relatively high demand rate of 7 liters oxygen(NTP)/minute for a pul monary or cardiac patient, and is approximatelyequal to the maximum rate at which oxygen could be supplied by the priorart system of US. Pat. No. 3,199,303.

The preceding results indicate that with the allattitude gas reliefcircuit of this invention, thegcryogenic liquid storage-dispensingcontainer remains operable even after being placed in a horizontalposition for an extended period of time. It has been demonstrated thatthe all-attitude gas relief circuit has the capability of preventingcryogenic liquid discharge, and the overall size of the liquidcontainer-vaporizing and gas vent control circuit assembly is notsignificantly increased by the all-attitude gas relief circuit.

The key dimensions of the assembly comprising the liquid oxygenstorage-dispensing container, vaporizing and gas vent control circuit,and all-attitude gas vent control circuit used in the aforedescribedtest are set forth in Table 1.

TABLE 1 KEY DIMENSIONS OF THE ASSEMBLY Characteristic SpecificationStorage-Dispensing Container 10):

Capacity, Liquid Oxygen 3 lbs. Capacity, Equivalent Oxygen Gas (NT?)1026 liters Inner Diameter (inches) 3.96 Wall Thickness (inches)0018-.030 Height (inches) 8-7/32 Overall Assembly:

Height (inches) 13% Width (inches) 9-11/32 Depth (Thickness) 5% OxygenGas Withdrawal Rates 1,2,3,4,5,6,7 (through valve 31): liters/min.

Normal Evaporation Rate: 0.34lb O /day Gas Vent-Liquid Fill Conduit(16):

Inner Diameter (inches) 0.1 13 Outer Diameter (inches) 0 125 LiquidWithdrawal-Gas Vent Conduit (21 )1 Inner Diameter (inches) 0.1675 OuterDiameter (inches) 0.1875

First Atmospheric Vaporizer (26):

Inner Diameter (inches) 0186 Outer Diameter (inches) 0.250 Length (feet)16-18 Second Atmospheric Vaporizer (35):

Inner Diameter (inches) 0.186 Outer Diameter (inches) 0.250 Length(feet) 2 First Orifice (63) Diameter (inches) 0.016

Second Orifice (64) Diameter (inches- 0.026

First Orifice (63) 0.016

Diameter (inches) Second Orifice (64) 0.026

Diameter (inches) Second Relief Valve (36) 52 psig Set Point Pressure(psig) First Relief Valve (32) 68 psig Set Point Pressure (psig)Bursting Disk (38) psig Set Point Pressure (psig) Maximum Vent Rate forSecond 17.5

Relief Valve/Normal Evaporation Rate Heat Transfer Capacity 1/8.5

Second Atmospheric Vaporizer/ First Atmospheric Vaporizer Vent Rate forSecond Relief Referring now to the assembly drawing of FIGS. 5-7, thesame identification numerals have been used for elements correspondingto elements in the schematic drawing of FIG. 3, and the system operatesin the previously described manner. The entire functional assembly isinside carrying case 70. Also, phase separator assembly 71 insures thatany entrained liquid inadvertently discharged through valve 27 during afill will not be sprayed outside carrying case 70. Such liquid will beseparated from high velocity vapor and fall harmlessly to the bottom ofthe enclosure.

Although certain embodiments have been described in detail, it will beappreciated that other embodiments are contemplated and thatmodifications of the disclosed features are within the scope of theinvention.

What is claimed is:

1. In a cryogenic liquid storage-gas supply system including a thermallyinsulated cryogenic liquid storagedispensing containing having top andbottom ends and being invertible between top-up dispensing and bottom-upfilling positions, gas vent-liquid fill conduit means with a first endterminating in the container top end and a second end outside saidcontainer top end, liquid withdrawal-gas vent conduit means with a firstend terminating in the container bottom end and a second end outsidesaid container top end, an invertible liquid vaporizing-gas vent controlcircuit outside the container and joined at a first inlet end to theliquid withdrawal-gas vent conduit means second end and including afirst atmospheric vaporizer, and gas flow regulating means between saidfirst atmospheric vaporizer and the gas discharge other end of saidcircuit: the improvement of an all-attitude gas relief circuit for saidcontainer comprising (a) first pressure relief means between said firstatmospheric vaporizer and said gas flow regulating means, (b) branchconduit means having one end in flow communication with the gasvent-liquid fill conduit second end, (c) second flow restrictionpressurerelief means in branch conduit (b) constructed to vent gas at lowerpressure than said first pressure relief means and at maximum ratebetween 3 and 25 times the normal evaporation rate from the container,and (d) a second atmospheric vaporizer in flow communication at itsinlet end with the branch conduit (b) one end and in flow communicationat its discharge end with the second flow restriction-pressure reliefmeans, and constructed with a heat transfer capacity not greater thanone-third the first atmospheric vaporizer capacity and also sufficientto vaporize cryogenic liquid entering its inlet end and discharge gas atrate between 1.04 and 1.30 times the maximum vent rate of 2. A cryogenicliquid storage-gas supply system according to claim 1 wherein the secondflow restrictionpressure relief means is constructed to vent gas atmaximum rate between and 20 times the normal evaporation rate from thecontainer.

3. A cryogenic liquid storage-gas supply system according to claim 1wherein the second atmospheric vaporizer heat transfer capacity is notgreater than onefifth the first atmospheric vaporizer capacity.

4. A cryogenic liquid storage gas supply system according to claim 1wherein the second atmospheric vaporizer heat transfer capacity issufficient to vaporizer cryogenic liquid entering the inlet end anddischarge gas at rate between 1.08 and 1.25 times the maximum vent rateof (c).

5. A cryogenic liquid storage-gas supply system according to claim 1wherein a pressure relief valve and a separate flow restriction elementin flow communication with each other comprise the second flowrestriction-pressure relief means (c).

6. A cryogenic liquid storage-gas supply system according to claim 1wherein a pressure relief valve and a porous member in downstream flowcommunication with said pressure relief valve comprise the second flowrestriction-pressure relief means (c).

7. A cryogenic liquid storage-gas supply system according to claim 1wherein the second flow restrictionpressure relief means is constructedto vent gas at maximum rate between 5 and 20 times the normalevaporation rate from the container, the second atmospheric vaporizer isconstructed with a heat transfer capacity not greater than one-fifth thefirst atmospheric vaporizer capacity and also sufficient to vaporizecryogenic liquid entering its inlet end and discharge gas at ratebetween l.08 and 1.25 times the maximum vent rate of (c), and wherein apressure relief valve and a porous member in downstream flowcommunication with said pressure relief valve comprise the second flowrestriction-pressure relief means (0).

8. In a method for supplying gas from a thermally insulated cryogenicliquid-storage-dispensing container having top and bottom ends and beinginvertible between top-up dispensing and bottom-up filling positions andwherein during the gas supplying step cryogenic liquid flows by overheadvapor pressure upwardly from the lowest zone of the container,discharged from the container top end and vaporized by atmospheric heatto form thegas supply, the improvement comprising: in a top-updispensing position,

a. when gas is not being supplied, venting vapor through a passage fromthe highest zone of the container, at flow-restricted maximum ratebetween 3 and 25 times the normal evaporation rate from the container,warming the vapor by atmospheric heat and discharging the warmed vaporwhen the container pressure is above a first lowest superatmosphericrelief pressure; and

b. when gas is being supplied, flowing cryogenic liquid by overheadvapor pressure upwardly from the lowest zone of the container,discharging such liquid from the container top end, vaporizing thesodischarged liquid by atmospheric heat, warming the vapor andwithdrawing the warmed vapor as the gas supply and simultaneouslyventing vapor in accordance with step (a); and

c. in a non-vertical position such that liquid flows through the passageof step (a) and the container gas pressure rises above the first lowestsuperatmospheric relief pressure: discharging first liquid from thenormally top end of the container at a first lower flow restricted rate,vaporizing the discharged first liquid, warming the cold first vapor toambient temperature and releasing the warmed first vapor at pressureabove said first lowest superatmospheric relief pressure; and when thecontainer pressure rises to a second higher superatmospheric reliefpressure between 1.08 and 1.75 times the first superatmospheric reliefpressure on an absolute basis, simultaneously discharging second liquidfrom the normally bottom end of the container at a second higher rate,vaporizing the discharged second liquid by atmospheric heat, warming thecold second vapor and releasing the 18 10. A method according to claim 8wherein said second higher superatmospheric relief pressure is between1.15 and 1.4 times the superatmospheric relief pressure on an absolutebasis.

1. In a cryogenic liquid storage-gas supply system including a thermallyinsulated cryogenic liquid storage-dispensing containing having top andbottom ends and being invertible between top-up dispensing and bottom-upfilling positions, gas vent-liquid fill conduit means with a first endterminating in the container top end and a second end outside saidcontainer top end, liquid withdrawal-gas vent conduit means with a firstend terminating in the container bottom end and a second end outsidesaid container top end, an invertible liquid vaporizing-gas vent controlcircuit outside the container and joined at a first inlet end to theliquid withdrawal-gas vent conduit means second end and including afirst atmospheric vaporizer, and gas flow regulating means between saidfirst atmospheric vaporizer and the gas discharge other end of saidcircuit: the improvement of an all-attitude gas relief circuit for saidcontainer comprising (a) first pressure relief means between said firstatmospheric vaporizer and said gas flow regulating means, (b) branchconduit means having one end in flow communication with the gasventliquid fill conduit second end, (c) second flow restrictionpressurerelief means in branch conduit (b) constructed to vent gas at lowerpressure than said first pressure relief means and at maximum ratebetween 3 and 25 times the normal evaporation rate from the container,and (d) a second atmospheric vaporizer in flow communication at itsinlet end with the branch conduit (b) one end and in flow communicationat its discharge end with the second flow restriction-pressure reliefmeans, and constructed with a heat transfer capacity not greater thanonethird the first atmospheric vaporizer capacity and also sufficient tovaporize cryogenic liquid entering its inlet end and discharge gas atrate between 1.04 and 1.30 times the maximum vent rate of (c).
 2. Acryogenic liquid storage-gas supply system according to claim 1 whereinthe second flow restriction-pressure relief means (c) is constructed tovent gas at maximum rate between 5 and 20 times the normal evaporationrate from the container.
 3. A cryogenic liquid storage-gas supply systemaccording to claim 1 wherein the second atmospheric vaporizer heattransfer capacity is not greater than one-fifth the first atmosphericvaporizer capacity.
 4. A cryogenic liquid storage gas supply systemaccording to claim 1 wherein the second atmospheric vaporizer heattransfer capacity is sufficient to vaporizer cryogenic liquid enteringthe inlet end and discharge gas at rate between 1.08 and 1.25 times themaximum vent rate of (c).
 5. A cryogenic liquid storage-gas supplysystem according to claim 1 wherein a pressure relief valve and aseparate flow restriction element in flow communication with each othercomprise the second flow restriction-pressure relief means (c).
 6. Acryogenic liquid storage-gas supply system according to claim 1 whereina pressure relief valve and a porous member in downstream flowcommunication with said pressure relief valve comprise the second flowrestriction-pressure relief means (c).
 7. A cryogenic liquid storage-gassupply system according to claim 1 wherein the second flowrestriction-pressure relief means is constructed to vent gas at maximumrate between 5 and 20 times the normal evaporation rate from thecontainer, the second atmospheric vaporizer is constructed with a heattransfer capacity not greater than one-fifth the first atmosphericvaporizer capacity and also sufficient to vaporize cryogenic liquidentering its inlet end and discharge gas at rate between 1.08 and 1.25times the maximum vent rate of (c), and wherein a pressure relief valveand a porous member in downstream flow communication with said pressurerelief valve comprise the second flow restriction-pressure relief means(c).
 8. In a method for supplying gas from a thermally insulatedcryogenic liquid-storage-dispensing container having top and bottom endsand being invertible between top-up dispensing and bottom-up fillingpositions and wherein during the gas supplying step cryogenic liquidflows by overhead vapor pressure upwardly from the lowest zone of thecontainer, discharged from the container top end and vaporized byatmospheric heat to form the gas supply, the improvement comprising: ina top-up dispensing position, a. when gas is not being supplied, ventingvapor through a passage from the highest zone of the container, atflow-restricted maximum rate between 3 and 25 times the normalevaporation rate from the container, warming the vapor by atmosphericheat and discharging the warmed vapor when the container pressure isabove a first lowest superatmospheric relief pressure; and b. when gasis being supplied, flowing cryogenic liquid by overhead vapor pressureupwardly from the lowest zone of the container, discharging such liquidfrom the container top end, vaporizing the so-discharged liquid byatmospheric heat, warming the vapor and withdrawing the warmed vapor asthe gas supply and simultaneously venting vapor in accordance with step(a); and c. in a non-vertical position such that liquid flows throughthe passage of step (a) and the container gas pressure rises above thefirst lowest superatmospheric relief pressure: discharging first liquidfrom the normally top end of the container at a first lower flowrestricted rate, vaporizing the discharged first liquid, warming thecold first vapor to ambient temperature and releasing the warmed firstvapor at pressure above said first lowest superatmospheric reliefpressure; and when the container pressure rises to a second highersuperatmospheric relief pressure between 1.08 and 1.75 times the firstsuperatmospheric relief pressure on an absolute basis, simultaneouslydischarging second liquid from the normally bottom end of the containerat a second higher rate, vaporizing the discharged second liquid byatmospheric heat, warming the cold second vapor and releasing the warmedvapor at pressure above said second superatmospheric relief pressure. 9.A method according to claim 8 wherein vapor is vented during step (a) atflow-restricted maximum rate between 5 and 20 times the normalevaporation rate from the container.
 10. A method according to claim 8wherein said second higher superatmospheric relief pressure is between1.15 and 1.4 times the superatmospheric relief pressure on an absolutebasis.